Atrio-Ventricular Septal Defect
One great view to visualize the atrioventricular valve (s) is in subcostal short-axis view. The atrioventricular valve(s) are not called mitral or tricuspid. They are usually on the same plane (usually the tricuspid valve is lower than the mitral from the Cranial to caudal plane).
Type A: Most common type in Down syndrome (Trisomy 21). The superior bridging leaflets are inserted on to the LV by chordal attachments.
Type B: Least common. The superior bridging leaflets attach to the RV by chordal insertion.
Type C: Associated with Transposition of great arteries and Tetralogy of Fallot. The superior bridging leaflets have no chordal insertions and are free-floating.
To learn more on atrio-ventricular canal - click here.
To learn more on fetal atrio-ventricular septal defect - click here.
Great review of AVSD here, with Rastelli Classification: https://thoracickey.com/atrioventricular-septal-defects-6/
Check out: https://www.wikidoc.org/index.php/Atrioventricular_septal_defect_classification
The Rastelli classification of atrioventricular septal defect (AVSD) categorizes the anatomy of the common AV valve based on how the chordal attachments of the valve relate to the ventricular septum. This classification is important for surgical planning and determining the complexity of repair.
Rastelli Types of AVSD:
Type A (Most Common)
The superior bridging leaflet is split at the level of the ventricular septum.
The left superior (anterior) leaflet (LSL) remains entirely within the left ventricle, while the right superior (anterior) leaflet (RSL) is positioned exclusively within the right ventricle.
Type B (Rare)
The superior bridging leaflet is divided and attaches to a papillary muscle in the right ventricle.
The abnormal papillary muscle attachment originating from the right side of the ventricular septum connects to the left portion of the common superior (anterior) bridging leaflet.
This type is extremely rare and is often associated with heterotaxy syndromes.
Surgical repair can be more complex due to abnormal chordal distribution.
Type C - Click here for example
The superior bridging leaflet remains intact and free-floating, without septal attachment. This type features significant bridging of the ventricular septum by the superior (anterior) bridging leaflet (SL), which remains intact and does not divide. It is free-floating without any chordal attachments to the septal crest. The posterior common leaflet may either be divided or undivided, but in most cases, it is well anchored.
This leads to a large communication between the left and right ventricles.
Surgical correction is more challenging, requiring careful reconstruction of the left AV valve to ensure competent function.
Presentation by Elissa Remmer and Stephanie Mardakis on Atrio-Ventricular Septal Defect

Case 1
Case 2
Due to the often concomittant "goose-neck" deformity of the LV outflow tract, it is important to rule out LV outflow tract obstruction and/or coarctation in cases of AVSD.